roles/postfix: Vary shlib directory by arch

The value of the `shlib_directory` is dependent the system architecture.
Specifically, x86_64 machines use `/usr/lib64/postfix`, while everything
else uses `/usr/lib/postfix`. This role was originally deployed on a
Raspberry Pi, so the original path was correct. Attempting to deploy it
on an x86_64 machine revealed the error.

This commit adds a new task that loads a variables file based on the
architecture. Each option defines an `arch_libdir` variable, which can
be expanded in the `postfix_shlib_directory` variable as needed.

roles/postfix/tasks/main.yml

@@ -1,3 +1,8 @@
+- name: load architecture-specific values
+  include_vars: '{{ item }}'
+  with_first_found:
+  - '{{ ansible_architecture }}.yml'
+  - default-architecture.yml
 - name: load distribution-specifc values
   include_vars: '{{ item }}'
   with_first_found:

roles/postfix/vars/default-architecture.yml

@@ -0,0 +1 @@
+arch_libdir: lib

roles/postfix/vars/defaults.yml

@@ -5,4 +5,4 @@ postfix_compatibility_level: 2
 postfix_sample_directory: /usr/share/doc/postfix/samples
 postfix_readme_directory: /usr/share/doc/postfix/README_FILES
 postfix_meta_directory: /etc/postfix
-postfix_shlib_directory: /usr/lib/postfix
+postfix_shlib_directory: /usr/{{ arch_libdir }}/postfix

roles/postfix/vars/x86_64.yml

@@ -0,0 +1 @@
+arch_libdir: lib64